Dissemination of IT for the Promotion of Materials Science (DoITPoMS)

DoITPoMS Micrograph Library Full Record for Micrograph 11

Full Record for Micrograph 11

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Micrograph no
Brief description
Cu 70, Ni 30 (wt%), cored dendrites
alloy Link to MATTER Glossary entry for alloy, copper, coring Link to MATTER Glossary entry for coring, dendrite Link to MATTER Glossary entry for dendrite, metal, nickel, partition coefficient Link to MATTER Glossary entry for partition coefficient
Metal or alloy
Cu-Ni   Link to phase diagram
Cu 70, Ni 30 (wt%)
Standard codes
Chill cast
Sample preparation
Etched in NH4OH/H2O2
Reflected light microscopy
Length bar
80 μm
Further information
This alloy is typical of many copper based alloy systems. The dendrite structure shows coring (variation in solute concentration). The light areas are rich in nickel and the darker areas are low in nickel. Chill casting extracts heat quickly enough to prevent significant solid state diffusion, resulting in cored dendrites. The centres of the dendrites that cool near the liquidus temperature, are nickel rich compared to the outer layers that solidify at progressively lower temperatures. Because the partition coefficient is positive the outer layers solidify with progressively lower nickel concentrations. The observed pattern results from the intersection of the plane of polish and the randomly orientated regions of equal solute concentration.
Prof T W Clyne
Department of Materials Science and Metallurgy, University of Cambridge
Licence for re-use
Attribution-NonCommercial-ShareAlike 4.0 International
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